The present invention relates to a method of spot-facing a printed board.
A printed circuit board used in an IC card or the like is spot-faced, and a part of an electronic part is sunk in the printed circuit board so as to make the IC card or the like thin and to enhance the reliability of the attachment of the electronic part.
The method for spot-facing a printed circuit board, as mentioned above, is conducted with the use of an endmill or other special purpose machine tools after the steps of drilling, plating and etching for preparing a desired circuit being carried out. Then, as shown FIGS. 3A and 3B circuitry 2 formed on a substrate of the printed circuit board P is extended in part into an area 3 to be spot-faced but a machining error is inevitably built up before the spot-facing process.
Accordingly, in the spot-facing process for the printed circuit board P, not only the circuit board 1 but also the circuitry 2 is cut and removed within the area 3 to be spot-faced so as to form a spot-face 4.
Further, during the spot-facing process, as shown in FIG. 5, when the circuitry 2 within the area 3 to be spot-faced is cut, the width w of the circuitry 2 becomes narrower and narrower as a tool 5 is advanced. Then, the pressing force of the tool 5 becomes larger than the bonding force of the circuitry 2 which therefore peels off from the substrate 1 so as to form burrs, these burrs being left on the circuit board 1, causing a short-circuit between the circuitry 2.
In order to solve such a problem, it has been proposed to cover an area to be spot-faced and an area therearound on a printed circuit board with synthetic resin before carrying out spot-facing process. With this process, the bonding force between the substrate 1 and the circuitry 2 is strengthened, and accordingly, occurrence of burrs can be eliminated.
However, the above-mentioned spot-facing process using synthetic resin for covering an area to be spot-faced, requires extra steps of, such as, coating the area with synthetic resin, drying the synthetic resin, removing the resin after completion of the spot-facing step, and drying the area, and the like, and accordingly, not only the workability is lowered but also machines and tools necessary for these respectively steps are prepared.